A number of systems for collecting and removing salts from crystallizers have heretofore been proposed. One interesting summary of previously used systems is disclosed in Canadian Department of Mines publication No. 325 entitled "REPORT ON THE SALT DEPOSITS OF CANADA AND THE SALT INDUSTRY," by L. H. Cole, issued in 1915. Such systems primarily consisted of a calandria type crystallizer with a salt basket chamber attached therebelow. The the salt basket was generally mounted on the ground or at a working platform. Typically, those crystallizers and the attached salt baskets were used for recovering crystals of highly solubility salts (those which (a) form highly concentrated solutions with water and which (b) are increasingly soluble at increasing temperature). Typically, the the salt was shoveled out of the salt basket through manually opening side doors.
Systems of the type identified above have been in use for about one hundred (100) years, and have mainly been used in the recovery and refining of various commercially utilized salts. The most significant use of such salt baskets has been with the manufacture of sodium chloride (NaCl), or table salt. Such heretofore known systems have the decided disadvantage that they offered few automatic operational features. Also, the removal of salt typically required substantial manual labor.
In so far as we are aware, the above described previously known salt baskets have not been utilized in combination with modern evaporator or brine concentration systems which distill the wastewaters at many industrial plants such as coal fired steam-electric generating plants, co-generation electrical generating facilities, metals smelting and refining facilities, pulp mills, chemical plants, and the like. Indeed, when such modern wastewater treatment systems have been unable to utilize large solar ponds for the discharge to and drying of the of concentrated brines and precipitated salts, recovery of the precipitated salts for disposal has been accomplished by resorting to the use of relatively expensive and otherwise undesirable alternatives such as filter presses, centrifuges, or spray dryers. Descriptions of such systems are found in a variety of trade publications, including: THE ECONOMICS OF WASTEWATER RECYCLING AT A LOS ANGELES COUNTY COGENERATION PLANT, by K. P Hammer, P. C. Egleston, Jr., and R. S. Ludlum, presented at WATERTECH 1992 in Houston, Tex., November 1992; CASE STUDIES: ZERO LIQUID DISCHARGE SYSTEMS AT THREE GAS-FIRED POWER PLANTS, by D. Bowlin and R. Ludlum, presented at the 1992 American Society of Mechanical Engineers COGEN TURBO POWER CONGRESS Meeting in Houston, Tex. in September, 1992; WATER MANAGEMENT FOR REUSE/RECYCLE, by S. D. Strauss, published in POWER Magazine, May, 1991; and EVAPORATOR AND SPRAY DRYER COMBINATION ELIMINATES RESIDUAL WASTEWATER LAGOONS, by R. McIntosh and A. E. Hodel, published in CHEMICAL PROCESSING, in February 1990.
The use of spray dryers, centrifuges, or filter presses for water solids recovery at zero discharge type wastewater treatment plants are not without disadvantages. Spray dryers consume large amounts of energy to evaporate residual brine from the solids being dried. In addition, in many jurisdictions, an air emissions permit is required for the discharge of heated air (normally including direct combustion products) which is vented from the spray dryer. Filter presses often consume expensive chemical additives in an attempt to increase the dryness of the residual salt cake. Centrifuges are rather expensive and the high speed rotating parts not infrequently require costly repairs. For both filter presses and centrifuges, it often seems that an inordinate amount of labor is expended to coax the systems through their required service, and unplanned additional maintenance requirements are a relatively common occurrence.